With the 2008 spike of gasoline prices to over $4 per gallon, a significant amount of focus has been placed on fuel economy (increasing miles per gallon (MPG)) in vehicles. A large variety of devices that save fuel, or at least claim to save fuel have been released as aftermarket addons. These devices include, but are not limited to: magnets, fuel catalysts, platinum injection, injection enhancers, air bleed devices, turbulence generators, atomizers, oil additives, fuel additives, engine cleaners, electrical modifications, hydrogen generators and aerodynamic modifications (list from www.fuelsaving.info).
The environmental protection agency has done studies on a number of these devices, and their effectiveness varies wildly. In addition to these devices, however, it is generally agreed that drivers can take certain steps to conserve fuel without changing the composition of their engine.
Several non-limiting examples of these steps include:    Slowing down—driving above 50 mph may use additional fuel, for example, it has been noted that driving just 10% about 50 mpg uses 10-20% more fuel.    Closing windows and removing roof racks—this reduces air resistance and should help increase efficiency.    Rolling up to stop lights instead of speeding up to them and stopping fully—if the light changes, the car will not need to be accelerated as greatly to resume a proper driving speed.    Removing excess weight from the car—carrying extra weight uses more fuel.    Keeping tires inflated—GOODYEAR estimates that a 20% underinflated tire uses 10% more fuel to run.
All these techniques may help improve the fuel efficiency of a vehicle. A whole class of drivers, referring to themselves as “hyper-milers” has emerged. National contests in fuel efficient driving are even being held in certain locations.
Additionally, vehicle sensors can often easily report fuel efficiency to drivers, and it may further be possible to be advised on a whole range of vehicle statistics due to sensor reports provided both in a car and online.